1. Field of the Invention
The present invention relates to a printed wiring board with improved corrosion resistance and yield.
2. Description of the Related Art
A width of a wiring pattern on a printed wiring board is made finer along with downsizing of electronic parts, and thus there is a problem in that the pattern is more difficult to form and a yield lowers during manufacture of the printed wiring board and a problem that disconnection easily occurs due to corrosion or electric corrosion in a field use environment. Particularly, there is a problem that a cutting fluid is misted in a factory where machines are used, the mist sticks to the printed circuit board surface, and thus wiring patterns leading from the parts' terminals disconnect due to corrosion or electric corrosion.
Japanese Patent Application Laid-Open No. 10-321115 discloses a technique for applying insulation coating which is excellent in corrosion resistance or moisture-proof property such as polyurethane resin on a printed circuit board. With this technique, in order to electrically connect the printed wiring board with electronic parts such as connector, the insulation coating needs to be applied after the parts are mounted. Thus, there is a problem that a coating material sticks to the electronic parts such as connector, which causes a contact failure.
Japanese Patent Application Laid-Open No. 2001-358445 discloses a technique for arranging blind via holes (BVH) in pads for surface-mount parts and forming leading wires (lines) in inner conductive layers. With this technique, when the blind via holes (BVH) are added to all the pads for mounting electronic parts, the wirings patterns concentrate on the inner conductive layers to which the blind via holes (BVH) are connected, and all the wires are difficult to connect.
Japanese Patent Application Laid-Open No. 2001-332851 discloses a technique for covering the outer peripheries of the pads with solder resist and eliminating exposure of wires leading from the pads. With this technique, the pad sides are not soldered, and thus there is a problem that a strength of soldering lowers.